A network is a collection of computing-oriented components that are interconnected by communication channels which permit the sharing of resources and information. Traditionally, networks have been physical networks, in which physical computing devices like computers are interconnected to one another through a series of physical network devices like physical switches, routers, hubs, and other types of physical network devices. More recently, particularly with the advent of virtual machine (VM) technologies that virtualize physical computing devices so that a number of such VMs can run on the same physical computing device, virtual networks have become more popular.
Virtual networks permit virtual devices and/or physical devices to communicate with one another over communication channels that are virtualized onto actual physical communication channels. In much the same way as a given physical computing device can support more than one VM, a physical network may support more than one virtual network. The virtual networks are separated from their underlying physical infrastructure and from one another, such as by using a series of virtual network devices like virtual switches, routers, hubs, and so on, which are virtual versions of their physical counterparts. A virtual overlay network in particular is a type of virtual network that is built on top of an underlying physical network.